1. Field of the Invention
The present invention relates to an image processing apparatus and a processing method therefor, and more particularly to an image processing apparatus for classifying the input image and converting it into density characteristics suitable for the kind of the image, and a processing method therefor.
2. Related Background Art
As a process function of an image input apparatus or an original copying apparatus, it is commonly executed to classify the input image data according to the kind of the image, and to execute a filtering process, a γ correction etc. suitable for the property of the original image to be processed, thereby improving the quality of the image.
There have been conceived various processing methods for classifying the kinds of the images. In most of these methods, a feature amount corresponding to the kind of the image is extracted and is evaluated by an evaluation function or a discrimination function determined in advance, thereby determining the kind of the image. The feature amount is often the generation frequently of black pixels or edges within a predetermined block area in the image, a histogram of the density levels, a spatial frequency distribution, or a directional distribution of lines.
The filtering process is to enhance or improve a localized feature of the image thereby improving the image quality of the original image, and includes an integrating filter for alleviating noise texture, and a differential filter for enhancing the edges in the image thereby providing the image with a more vivid feeling.
The γ correction executes tonal correction for the image density. Examples of tonal correction for the image density include a process of uniformly extending or compressing the dynamic range of the density values, and a non-linear conversion of extending or compressing a particular density range in contrast to other ranges.